PROJECT SUMMARY A number of adverse effects of blood transfusion persist. One is the recent recognition that adverse effects increase with time of storage of packed red cells (PC). This has led surgeons to demand only recent PC, an added strain on limited supply. The explanation for the adverse effects has been conjectural, but it is known that red blood cells (RBC) release microparticles (RMP) during storage, which accumulate with time. There is new evidence that RMP, like MP from other cell types, can be injurious, especially at high levels. Accordingly, the hypothesis underlying the proposal is that RMP contribute substantially to adverse effects of PC transfusion; and that removal of RMP prior to transfusion will reduce indicators of adverse effects. The study has two major aims. Aim 1 is to assess the potentially pathologic properties of RMP as they emerge in PC with time. Although MP from other cells have been studied extensively and linked to many disorders, RMP have been little studied and have not been considered to be hazardous. However, recent evidence indicates that they do have significant potential to cause harm, such as microvascular ischemias. The assays to be performed include MP- mediated thrombin generation, MP-bound complement components, and other prothrombotic and inflammatory markers. We will perform this time study on a total of 60 PC units, since significant donor variability has been observed. When sufficient data is accumulated (after year 2) from in vitro and patient study, selected groups of samples will undergo proteomic profiling in effort to identify the most hazardous components of RMP. Anticipated results. It is expected from prior work that time of storage will be the dominant factor of adverse properties of RMP. However, donor-specific adverse MP are also likely and will be investigated by proteomic study. Aim 2 is a clinical study to directly test the hypothesis by administering to randomized patients scheduled for coronary artery bypass surgery either conventional PC (Group 1) or PC washed prior to transfusion to deplete MP (Group 2). Patients who do not require transfusion will serve as patient controls (Group 3). The 4-year period will recruit n=500 patients, half of whom are randomized to Groups 1 and 2; and half of all subjects will not require transfusion (Group 3). The study is not designed to evaluate major transfusion reactions, which are rare. Differential effects between the groups will be assessed primarily by a panel of sensitive biomarkers capable of detecting subclinical but adverse responses such as endothelial injury, platelet activation, and other markers of inflammation, oxidation, and coagulation. Clinical responses, surgical outcomes, etc. will also be monitored and recorded. Anticipated results: It is expected that patients who received PC-MP will exhibit fewer or less severe complications and adverse biomarkers. The significance of the work is self-explanatory. The long-term objective is to improve transfusion safety.